DESI’s Commissioning Instrument has jump-started the commissioning process for DESI by tackling some of the basic but important tasks required to bring DESI online. It successfully tested the telescope control system (TCS), telescope guiding, the image optimization system, and DESI’s algorithm that maps between sky and fiber-positioner coordinates, also known as Platemaker.
The Commissioning Instrument was installed at the DESI focal plane behind the DESI Corrector during Spring 2019. Its focal surface consisted of five CCD sensors and 22 fiber-illuminated fiducials whose positions were engineered to work effectively with Platemaker. The surface was enclosed in a tall steel cylinder. The entire Commissioning Instrument was designed to have the same mass and mass distribution as DESI’s Focal Plane System to ensure realistic operations.
The Commissioning Instrument was installed at the Mayall Telescope and began a two-month commissioning run on April 1, 2019. During Summer 2019 it was removed to make way for the installation of the DESI Focal Plane System.